The present invention relates to semiconductor devices and fabrication methods thereof and, more particularly, to floating trap type non-volatile memory devices and to fabrication methods thereof.
A non-volatile memory device is an advanced type of memory device that retains information stored in its memory cells even when no power is supplied. Nowadays, the non-volatile memory device is widely used in various kinds of electronic products like as a cellular phone, a memory card and so on.
As one of the non-volatile memory devices, a floating trap type non-volatile memory device comprises a gate electrode, a semiconductor substrate and a floating trap region. The floating region is interposed between the gate electrode and the substrate. During device operation to store or erase date, electrons are trapped into the floating region or discharged from the floating region.
FIG. 1 is a schematic plan view illustrating a typical floating trap type non-volatile memory device.
FIGS. 2 through 5 are cross-sectional views illustrating successive process steps for forming a conventional non-volatile memory device. FIGS. 2 through 5 are taken along a line I-Ixe2x80x2 of FIG. 1. FIGS. 1 through 5 are drawings specifically illustrating a cell array area of the non-volatile memory device.
Referring to FIG. 2, a floating layer 108, a lower conductive layer 110 and a mask layer 112 are sequentially formed on a semiconductor substrate 100. The floating layer 108 comprises a lower dielectric layer 102, a charge storage layer 104 and an upper dielectric layer 106. Photoresist patterns 114 are formed on the mask layer 112.
Referring to FIGS. 1 and 3, the mask layer 112, the lower conductive layer 110, the floating layer 108 and the substrate 100 are continuously etched to form trenches 118, floating regions 108a, lower conductive strips 110a and masks 112a, wherein the photoresist patterns 114 are used as etching masks. The trenches 118 define active regions 116 in the substrate 100. Each of the floating strips, i.e., floating regions 108a comprises a lower dielectric strip 102a, a charge storage strip 104a and an upper dielectric strip 106a. Subsequently, the photoresist patterns 114 are removed and an isolation layer 120 is formed to fill the trenches 118.
Referring to FIGS. 1 and 4, a portion of the isolation layer 120 is removed to expose top surfaces of the masks 112a to form isolation regions 120a in the trenches 118.
Referring to FIGS. 1 and 5, the masks 112a are removed. Subsequently, an upper conductive layer is formed on the whole surface of the resultant structure. The lower conductive strips 110a and the upper conductive layer are patterned to form gate electrodes 124. The gate electrodes 124 are disposed across the trenches 118 and the active regions 116. Each of the gate electrodes 124 comprises a lower gate electrode 110b and an upper gate electrode 122. The upper gate electrode 122 is disposed across the trenches 118 and the active regions 116. The lower gate electrode 110b is located only between the upper gate electrode 122 and the floating strips 108a. 
Though not shown in the drawings, the floating regions, i.e., floating strips 108a optionally may be patterned by self-alignment techniques to the gate electrodes 124 thereby to form floating patterns 108b, which is located only between the gate electrode 124 and the active regions 116. Each of the floating patterns 108b comprises a lower dielectric pattern 102b, a charge storage pattern 104b and an upper dielectric pattern 106b. 
According to the conventional non-volatile memory device, the charge storage region i.e., the charge storage strip 104a or the charge storage pattern 104b has a high defect density on the sidewall thereof. This is due to an etching damage on the sidewall during the formation of the trenches 118. The defects on the sidewall of the charge storage region may act as leakage current paths at the boundary region between the isolation region and the floating region. Therefore, the stored charges in the charge storage region may be lost through the defects.
It is an object of the present invention to provide a semiconductor device having a floating region, wherein leakage current is substantially suppressed at the boundary region between an isolation region and the floating region, so that charge loss is substantially suppressed at the boundary region.
It is another object of the present invention to provide a method for fabricating a semiconductor device having a floating region, wherein leakage current is substantially suppressed at the boundary region between an isolation region and the floating region, so that charge loss is substantially suppressed at the boundary region.
According to one aspect of the present invention, a semiconductor device is provided. The semiconductor device comprises a gate electrode formed on a substrate. A floating region is interposed between the substrate and the gate electrode. The width of the floating region is wider than that of the gate electrode. The floating region comprises a charge storage region and the width of the charge storage region is wider than that of the gate electrode. The charge storage region is preferably formed of an oxidation resistive layer. The floating region is preferably formed of an ONO layer and the charge storage region is preferably formed of a silicon nitride layer of the ONO layer. The gate electrode comprises a lower gate electrode and an upper gate electrode. The width of the charge storage region is wider than that of the lower gate electrode. An isolation region defines an active region in the substrate. The upper gate electrode is extended across the isolation region and the active region. And, the lower gate electrode is interposed between the upper gate electrode and the active region.
According to another aspect of the present invention, a semiconductor device is provided. The semiconductor device comprises an isolation region formed on a substrate. The isolation region defines an active region in the substrate. A gate electrode is formed on the active region. A floating region is interposed between the active region and the gate electrode. The width of the floating region is wider than that of the active region. The floating region comprises a charge storage region and the width of the charge storage region is wider than that of the active region. The charge storage region is preferably formed of an oxidation resistive layer. The floating region is preferably formed of an ONO layer and the charge storage region is preferably formed of a silicon nitride layer of the ONO layer. The isolation region fills a trench in the substrate. The isolation region comprises a thermally grown trench oxide at the sidewall of the trench. The gate electrode comprises a lower electrode and an upper electrode. The upper gate electrode is extended across the isolation region and the active region. And the lower gate electrode is interposed between the upper gate electrode and the active region.
According to another aspect of the present invention, a semiconductor device is provided. The semiconductor device comprises an isolation region on a substrate. The isolation region defines an active region in the substrate. A gate electrode is formed on the active region. A floating region is interposed between the active region and the gate electrode. The floating region has a protrusion portion at an end thereof. The protrusion portion extends into the isolation region and the isolation region substantially surrounds the protrusion portion. The floating region comprises a charge storage region and the charge storage region has the protrusion portion at an end thereof. The charge storage region is preferably formed of an oxidation resistive layer. The floating region is formed of an ONO layer and the charge storage region is preferably formed of a silicon nitride layer of the ONO layer. The isolation region fills a trench in the substrate. The isolation region comprises a thermally grown trench oxide at the sidewall of the trench. The gate electrode comprises a lower electrode and an upper electrode. The upper gate electrode is extended across the isolation region and the active region. The lower gate electrode is interposed between the upper gate electrode and the active region. The isolation region comprises a thermally grown sidewall oxide at an end of the lower gate electrode.
According to another aspect of the present invention, a method for forming a semiconductor device is provided. The method comprises forming a floating strip on a portion of a substrate. The floating strip comprises a charge storage strip made of an oxidation resistive layer. A lower conductive strip is formed on the floating strip. The lower conductive strip has a sidewall. A trench is formed in another portion of the substrate. The trench has a sidewall and the trench defines an active region. A trench oxide is formed on the sidewall of the trench to reduce the width of the active region. A sidewall oxide is formed on the sidewall of the lower conductive strip to reduce the width of the lower conductive strip. An isolation pattern is formed to fill the trench. The width of the charge storage strip is greater that the width of the lower conductive strip and the width of the active region. The floating strip is preferably formed of an ONO layer and the charge storage strip is preferably formed of a silicon nitride layer of the ONO layer. The ONO layer comprising an upper silicon oxide layer which is a CVD oxide layer. The trench oxide and the sidewall oxide are formed by a thermal oxidation method. The formation of the isolation pattern comprises forming a mask on the lower conductive strip, forming an isolation layer on the mask and in the trench and removing a portion of the isolation layer to expose the mask. The mask comprises a material selected from the group consisting silicon nitride and silicon oxide. An upper conductive strip is formed on the lower conductive strip and the isolation pattern. The upper conductive strip is disposed across the isolation pattern and the active region. A portion of the lower conductive strip is removed to form a lower electrode. The lower electrode is located in an overlapping area of the upper conductive strip and the active region. The upper conductive strip is an upper electrode. The upper conductive strip is preferably made of polysilicon or polycide. The lower conductive strip is preferably made of polysilicon.